1. Field of the Invention
The present invention relates to stream control techniques for controlling packet-based streams composed of multiplexed video and audio, such as MPEG (Moving Picture Experts Group) streams, and particularly to a stream control technique in implementing multiple times of encryption/decryption for streams.
2. Description of Related Art
In step with recent spread of data communication networks, so-called home networks are being diffused in the home so that home appliances, computers, and other peripheral apparatuses are coupled via a network to allow communication among the apparatuses. In the home network, the communication among the network-coupled apparatuses allows sharing of data processing functions of the respective apparatuses. The home networks offer users convenience and comfort. For example, users are allowed to transfer content among network-coupled apparatuses. Therefore, it is anticipated that the home networks will become more popular in the future.
Digital transmission content protection (DTCP) is known as the de facto standard of a technique for protecting content copyrights in the home networks. In the DTCP, a content sender and a content receiver verify each other and exchange an encryption key to share it, so that encrypted data is transferred therebetween.
In many cases, plural apparatuses coupled to a home network employ not a single scheme of encryption/decryption but a plurality of schemes of encryption/decryption. For example, the DTCP/IP for developing the DTCP on an IP network employs advanced encryption standard (AES) of which key length is 128 bits as a standard. In contrast, recording of data in a medium such as a hard disk drive (HDD) employs data encryption standard (DES), of which cipher strength is lower than that of the AES.
In this manner, different multiple schemes of encryption/decryption are employed in the home network, and buffers (memories) that temporarily store stream data as content are provided among encryption/decryption processors. For example, Japanese Patent Laid-open No. 2003-281085 discloses a technique in which encrypted/decrypted data is transferred via memories as buffers.